What Makes Good Compost?

Most organics make fine compost that provide nourishment to plants.

Gardeners prize compost for its ability to foster long-term soil health. Regular applications of what some compost enthusiasts term "black gold" not only provides nutrients for your plants, it increases soil organic matter, which helps your soil hold water and nutrients, creating a friendly environment for beneficial soil microbes that help prevent plant diseases (see References 1, page 154). Using good materials and methods results in a good soil amendment for your garden.

What Goes In

Just about any material of organic origin eventually turns into fine compost. For the best results, you should add about two parts of carbon-rich "browns" for every one part of nitrogen-rich "greens." Greens include fresh materials like grass clippings and food scraps. Browns include long-dead ingredients like autumn leaves, paper, wood chips and sawdust. Don't overlook materials you might not immediately think of putting in your compost. Cotton and wool rags, teabags and coffee grounds, fireplace ashes, eggshells, cardboard and pet hair all contribute to your compost. (See References 2)

What Stays Out

For the best compost, you should avoid using meats, dairy, bones, and oily or greasy foods. Though they eventually break down, the process happens slowly; resulting odors can attract scavengers in the meantime. Plants infected with diseases or insect infestations should also be kept out, as should weeds with seeds or rhizomatous root systems, like buttercups and some grass species. Unless the compost pile heats up enough to destroy these garden invaders, you risk infecting your plants with disease or having a resurgence of weeds or bugs from using infected compost (see References 3, page 16). Also watch out for compost ingredients contaminated by herbicides or by pesticides that can harm the soil bacteria needed for breakdown (see References 2). Avoid the temptation to raid your neighbor's lawn for his grass clippings, as herbicides you're not aware of can cause stunted growth or death in garden plants. Likewise, use manures only when you know the animal's feed source hasn't been treated with herbicides (see References 4).

Aeration and Moisture

Although the fastest-producing microorganisms in compost require oxygen, you will eventually see breakdown even with an absence of air in your compost pile. However, anaerobic microorganisms create acids and alcohols as a byproduct, and these materials can harm your plants (see References 3, page 4). To encourage the microbes that make the best compost, ensure an air supply in the center of your compost pile. Periodically turning your compost lets in fresh air and fluffs the compost, creating air pockets. If you don't have time for turning, you can use an aerator to punch holes and deliver air to the center of the pile. If you squeeze a handful of in-progress compost, no more than a few drops of water should emerge. Too much moisture fills the air pockets in your compost and creates anaerobic conditions (see References 3, pages 7-8).

Using Manures

Livestock manures can boost the nutrient content of your compost. Rabbit and chicken manures provide the best source of nitrogen, while duck, rabbit and chicken manures rate above-average in phosphorus content. For a potassium boost, sheep manure tops that produced by all the other barnyard residents. (See References 1, page 371)